This invention relates generally to a ballast for a fluorescent lamp, and more particularly to a triac dimmable compact fluorescent lamp.
A triac dimmable ballast controls the amount of power supplied to and thereby the level of illumination provided by a fluorescent lamp. A conventional triac dimmable ballast, such as disclosed in U.S. Pat. No. 4,392,086, does not include an electromagnetic interference (EMI) filter. The EMI filter removes harmonics generated by the ballast. These harmonics, especially during turn on of the triac when the ballast is set to high dim levels, can reduce the current drawn by the ballast to zero earlier than desired. Premature turn off of the triac can result. The ballast through this premature turn off of the triac is unable to draw current for a significant portion of the 60 hertz (Hz) half cycle of the mains voltage. The lamp is unable to achieve the desired level of illumination.
Other conventional compact fluorescent lamps, such as disclosed in U.S. Pat. No. 5,313,142, include EMI filters but when coupled to a triac are ineffective in preventing the premature turn off of the triac due to the generation of harmonics produced by the ballast. The restriction in size and number of components within a compact fluorescent lamp makes it difficult to effectively filter these harmonics without exceeding space requirements.
Accordingly, it is desirable to provide an improved compact fluorescent lamp whose level of illumination can be set through use of a triac dimmer. The improved compact fluorescent lamp should effectively filter harmonics produced therein to preclude premature turn off of the triac dimmer especially when set at high dim levels.